In sensor network systems, numerous wireless sensor nodes detect changes in the environment of an area where the sensor nodes are disposed. Further, according to a commonly known technique, data is transmitted by relayed transfer through multihop communication among sensor nodes to a sensor node that is not directly connected.
According to a conventional technique, when relayed transfer is performed, information of whether a relay process is being performed with nearby sensor nodes is periodically exchanged. When no nearby node is performing a relay process, a reception function is continuously in an operating state and when a relay terminal is present, the reception function is in a sleep state excluding periodic reception intervals (for example, refer to Japanese Laid-Open Patent Publication No. 2011-49676). Thus, an aggregation process is performed by a portion of the sensor nodes.
According to another conventional technique, to reduce power consumption, an interval for the sleep state is determined based on remaining energy information and sleep information of adjacent nodes (for example, refer to Japanese Laid-Open Patent Publication No. 2004-336779).
According to another conventional technique, in a sensor network that transfers data by multihop communication, terminals are grouped according to distance from a base station and set to be in the sleep state except when communicating at constant intervals. When a terminal detects emergency information, the cycle at which information is sent is shorted (for example, refer to Japanese Laid-Open Patent Publication No. 2009-86697).
Nonetheless, with the conventional techniques, a problem arises in that, for example, when the sensor nodes are operated intermittently, to enable the sensor nodes to give notification of a detected abnormality even during an idle period, reception circuits of the sensor nodes are in operation during the idle period and consequently power consumption becomes great.